This invention relates to devices and methods for reducing the volume of aqueous waste effluents containing dissolved solids, such as developer, fixer and/or wash water from processing photosensitive materials.
Various aqueous waste effluents containing dissolved solids, such as developer, fixer and/or wash water from processing photographic film, X-ray film, graphic art materials and the like, often include amounts of undesirable chemicals, such as silver, lead, ferrocyanide, thiosulfates and organic materials, above that permitted by federal, state and/or local government regulations for disposal in open bodies of water, muicipal sewers, septic tanks, etc. Consequently, such waste effluents are considered hazardous or do not meet local sewer codes and require special handling and disposal techniques which can be quite expensive.
Three general approaches have been used for removing hazardous constituents from such effluents. In one approach, the effluent is circulated through one or more resin columns and the toxic constituents collect on the resin. The columns must be periodically treated to strip the collected constituents from the resin. In a second approach, the effluent is charged with a small electrical charge which causes metal ions to disassociate and form a slurry which may be collected and refined to recover silver and other valuable metals. In a third approach, the effluent is heated to gradually evaporate water and to form a sludge which can be disposed of, or in some cases, can be refined to recover the valuable metals.
The evaporate approach is advantageous for applications generating smaller volumes of aqueous waste effluents because of the relatively low initial and operational cost for the equipment and the equipment does not require a large amount of space. Prior evaporative systems have one or more shortcomings. One type prior system must be periodically shut down to physically remove the sludge from the evaporative unit. Another type includes means for pumping the slurry into a barrel for disposal. However, the sludge produced by both type prior systems is considered a hazardous waste under some government regulations because of the water content and, therefore, special handling and disposal requirements must be met. The residual water increases the volume of material to be handled, transported and/or disposed. In some cases, residual water must be removed from the sludge before it can be refined to recover valuable metals or disposed.